Researchers have unprecedentedly discovered the mechanism through which fish are able to sense the seasons and when it is time to spawn.

Japanese scientists Nagoya University and from Utsunomiya University found that a previously puzzling area of the brain in salmon informs the fish of changes in the length of the day that come with each season.

The results of the study were published this week in the online British scientific journal Nature Communications.

The group of researchers analysed the masu salmon, whose stocks spawn in the autumn, to determine if seasonally breeding fish use a mechanism similar to that of birds and mammals, which have sensors that produce the secretion of hormones that grow testes as the days get longer, The Asahi Shimbun reports.

Appropriate conditions then turn on the production of reproductive hormones that induce fertility and tell the fish it is spawning season.

The researchers divided 20 salmon into two groups and raised them for two months, one group illuminated for 16 hours a day representing summer, and the other for eight hours a day representing winter. After subsequently examining the fishes’ brain tissue, it was found that an area called the saccus vasculosus behaved as a sensor for light.

Scientists then removed the saccus vasculosus from some fish and saw that the testes did not grow as expected in those fish under the artificial conditions and that certain hormones were not secreted.

This means that the saccus vasculosus serves as a sensor for fish to detect which season is approaching and, in the case of autumn, induce breeding, the scientists explained.

These findings regarding how exactly fish perceive seasons and how this affects their brains and hormonal activity may lead to improved breeding programmes and be applicable in other industries, said Takashi Yoshimura, a professor of animal physiology at Nagoya University and a member of the research group.

“It is well established that day length is the dominant seasonal cue for many organisms. But, temperature changes also affect the seasonality in some species. I would like to understand how animals sense changes in temperature to adapt to seasonal changes in environment,” Yoshimura added, according to Asian Scientist.

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